This invention relates to fluorinated electrolyte salts useful in battery electrolyte compositions.
Electrolyte salts for use in electrochemical cells, e.g., lithium or lithium ion cells, must exhibit good ionic conductivity, electrochemical stability, thermal stability, and chemical stability. In addition, the components of the electrochemical cell must be stable towards the electrolyte. Stability concerns are particularly acute in the case of electrochemical cells having aluminum cathode current collectors because the aluminum is susceptible to corrosion.
Among the known electrolyte salts, lithium bis(trifluoromethanesulfonyl)imide ((CF.sub.3 SO.sub.2).sub.2 N.sup.- Li.sup.+) has excellent conductivity and stability, but is highly corrosive. LiPF.sub.6 has excellent conductivity and is not corrosive, but is thermally and hydrolytically unstable. LiO.sub.3 SCF.sub.3 (also called lithium triflate) has good thermal and chemical stability, but has low conductivity and is highly corrosive.
Indeed, the corrosion of aluminum in electrolytes containing lithium triflate or lithium bis(trifluoromethanesulfonyl)imide is so severe as to make these salts of little use for applications in the more advanced, high voltage cells. Thus, the use of presently-available electrolyte salts in high voltage lithium or lithium-ion cells has resulted in batteries having suboptimal performance characteristics such as restricted operating temperature ranges and limited discharge/charge rates and inadequate cycling performance, particularly when aluminum components are used.